The present invention relates in general to sheet feeding apparatus, and more particularly, to a friction sheet feeding apparatus including a vacuum assist mechanism to improve the overall reliability of the sheet feeding apparatus.
Modern reproduction equipment, such as copiers or printers or the like, are capable of operating at very high speeds. In order to assure that the equipment functions in a manner to reliably produce desired copies of original information, such equipment must include sheet feeding apparatus for handling original information-containing document sheets and sheets of receiver material for rapid, reliable transport through the equipment. The sheet feeding apparatus must operate to feed sheets at the necessary high transport speeds without damage to the sheets, and with a maximum of stoppages due to misfeeds or multifeeds.
Sheet feeding apparatus for carrying out the desired high speed reliable transport typically employ either friction or vacuum feeding devices for separating individual sheets from a sheet stack for transport through the reproduction equipment. Friction sheet feeders utilize a friction member to scuff a sheet to remove such sheet from the top or bottom of a stack of sheets. On the other hand, vacuum feeding devices include a member which attracts the top or bottom sheet from a sheet stack by application of vacuum forces to the member. The member, and the attracted sheet, is then moved to remove the sheet from the stack.
While both friction and vacuum type feeding devices can be designed to be generally reliable, each have certain inherent inadequacies. Particularly, friction devices are highly dependent upon the frictional characteristics of the material being fed. It is therefore difficult to design a single friction feed device which can, without substantial adjustment, accommodate reliably all the different materials used as original sheets or receiver materials which the reproduction equipment may have to handle. On the other hand, vacuum devices are highly dependent on other characteristics of the material being fed, such as their weight or porosity for example. Such devices require significant control mechanisms to provide optimum vacuum to reliably feed single sheets without misfeeds or multifeeds.